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DEPARTMENT OF IMMUNOBIOLOGY
Antibody (Ab)Antibody (Ab)
Xiaowu Hong
xiaowuhong@fudna.edu.cn021-54237093
Department of ImmunologyShanghai Medical College of Fudan University
Emil von Behring, 1901, antitoxins
Georeges Kohler and Cesar Milstein, 1984, monoclonal antibody
Susumu Tonegama,1987, structure of Ig gene
Gerald Edelman and Rodney Porter, 1972, structure of antibody
Paul Ehrlich , 1908, production of antibody
Nobel Prize winners
Emil von Behring (1845-1917)
Emil von Behring, 1901, antitoxins
I Definition of antibodyI Definition of antibody
II Structure of antibody II Structure of antibody
III Function of antibody III Function of antibody
IV Biological characteristics of different antibodies IV Biological characteristics of different antibodies
Contents
Antibody (Ab) A globulin which is produced by plasma cell as a result of the introduction of an antigen and which has the ability to combine with the antigen that stimulated its production.
Immunoglobulins (Ig) Globulins composed of H and L chains, or globulins function as antibody. Immunoglobulins
Antibody-containing serum is place in an electrical field
Antibodies migrated with the globular proteins.
All antibodies are immunoglobulins, but it is not certain that all immunoglobulins have antibody function.
The relationship between Ab & Ig
Antibody molecules are found in serum
(account for approximately 20% of the t
otal plasma protein ), in extravascular flui
ds, in exocrine secretions, and on the suon the su
rfacerface of some lymphocytes.
Distribution of antibody
Section 1 Structure of Ig
* A four polypeptide chains: two identical light chains two identical heavy chains , held by disulfide bonds.
** Y-shape structure, symmetric.
*** –NH2 terminal, -COOH terminal.
**** variable & constant regions.
***** domains
1 Basic four chain structure
(1)Heavy chain (H): ① Composed of about 500 aa, oligosaccharide
(+) ② Class :
heavy chain , , , , . immunoglobulin(Ig) IgA, IgG, IgM IgD, IgE
(2) Lght chain (L): ① Composed of about 214 aa, oligosaccharide(-) ② Type: ,
2 Variable (V) and Constant (C) regions
(1) V region ① N-terminal 1/2L+1/4(1/5)H;
VL, VH
(2) Constant region (C-terminal 1/2L+3/4(4/5)H)
CLCH1CH2CH3(CH4)
(complimentarity
determining re
gion, CDR) :
formation of the Ag binding site
Framework region ( FR ) :
maintaining the 3- dimensional configuration
(3) hypervarible region (HVR)
(complimentarity determining region,) CDR
purple : HV CDR ( in both the ribbon and ball and stick views)
green : antigen
HV sequences contact the antigen.
antibody
antigen antigen-antibody complex:
Representation of the disassociation of an antibody (top) and antigen (botton) molecule.
CDR
Epitope
antibody
antigen
(4) Hinge region
VH
CH1
CH2
CH3
CH4
VL
CL
Hinge region
COO–
NH3+
Properties:1) Flexible2) Rich in proline
Function:1) Facilitating the interaction between Ag and Ab2) Facilitating complement
fixation
(IgM CH3 , IgG CH2)
IgG Molecule Conformational Changes Induced by Antigen Binding
Fab
Fc
PREBINDING
CH1
CH2
Barricaded C1q-bindingsite
POSTBINDING
Exposed C1q-bindingsite
Flexibility of immunoglobulins
domains: polypeptide chains folded by disulfide bonds into globular regions.
domains:
FcR binding (mast, basophil)(IgE)CH2+CH3
C1q binding(IgM)CH3
FcR binding (MC, M, B,NK)(IgG)CH3
C1q binding(IgG)CH2
Allotypic markerCH1+CL
a Ag- binding siteVH+VL
Figure 3-3 part 1 of 2
3 Enzymatically generated Ab fragments
(1) Papain:
Fab (Ag-binding Fragment )
Fc (Crystallizable Fragment ) : complement fixation, FcR
Figure 3-3 part 2 of 2
( 胃蛋白酶 )(2) Pepsin( Fab’ ) 2
pFc ( peptides of Fc )
Section 2 Biological functions of antibodies
1 Antibody function in the absence of other factors
V region: Ag binding
•Neutralizing toxin & virus•Agglutination microbes,•Prevention adhesion
Neutralization By Antitoxin
Antibodies
Neutralization By Antiviral
Antibodies
Bacterial ‘Neutralization’ By Ab
C region:Fixation of complement
2 Role of antibodies in complement activation
C region:Binding cells Opsonization Mediating ADCC
3 Role of antibodies binding to effector cells
(1) Opsonization:
The process of attaching opsonins , such as IgG or complement fragments, to microbial surfaces to target the microbes for phagocytosis.
antibody
complement
CD16 CD16 (( FcFcR IIR IIII ))
CD11b/CD18
CD25
CD28
CD32 ( Fc R II )
CD35 ( CR1)
CD64 ( Fc R I )
CD71
B7-2
IL-2
antibody
antibody
Recognition of microbes by neutrophils and macrophages
complement
Lacto
ferrin
Surface receptor on
macrophage
Adherence of bacteria via receptors
Opsonin. A macromolecule that becomes attached to the surface of a microbe and can be recognized by surface receptors of neutrophils and macrophages and that increase the efficiency of phagocytosis of the microbe.
Opsonins include IgG antibodies, which are recognized by the Fc receptor on phagocytes, and fragment of complement proteins, which are recognized by CR1.
FcR and Complement Receptors Cooperate To Induce Greater Phagocytosis
FcRIII CD16
Antibody Marks Target Cells For NK Cell Attack
(ADCC)
(2) ADCC
Figure 1-24 part 2 of 3
Section 5 Biological characteristics of different antibodies
7.4.1
11 interchain disulfide bonds.
1 IgG
(1) Properties(A) IgG is the major Ig in serum - 75%(B) The longest half life (t ½ =23days)(C) IgG is the major Ig in extravascular spaces(D) Placental transfer(E) Fixation complement – (F) Binding to cells –Opsonization mediating ADCC
Immunity is transferred from
mother to fetus through place
ntal transfer of IgG.
(1) StructureSecreted IgM (sIgM): pentamerMembrane-bound IgM (mIgM): monomer
J chain
IgIg
IgIg
2 IgM
(1)Chemical nature: polypeptide chain secreted by plasma cell
(2) Presence: polymeric Igs such as IgM (pentamer), sIgA (dimer).
Joining chain
J CHAIN
IgM
IgA
Secrete piece
Joining chain
(2) Properties(A) The first Ig made by fetus and B cells
(B) Fixation complement –classical pathway
(C) The largest size of molecule
(D) Natural blood typeblood type antibody(E) Binding to cells –
Opsonization.
mediating ADCC
3 IgA(1) Structure
Secretory Piece ( SC )synthesized by nonmotible epithelial cells near the mucosal membrane
Function:i. Enabling IgA to be transported across mucosal tissues into secretions.
ii. Protecting sIgA from being proteolytic attack.
IgA dimer
Secrete piece
Joining chain
(2) Properties(A) The major Ig in secretions. (secretory IgA, sIgA. 5-15g/d)
(B) sIgA :transferred to the newborn through colostrum
(C) The important antibody against mucosal infections
(Local (Mucosal )immunity)
4 IgE(1) Structure
A) The least common Ig
B) Binds to basophils & mast cells (FcR)
(2) Properties
Involved in allergic reactions( hypersensitivity I)
(2) Properties
a. On the surface of mature B cell serving as BC
R mature marker of B cell
b. In serum (uncertain Ab
activity)
Immunoglobulin Isotypes Are Distributed To
Different Parts Of The Body
IgM – BloodIgG – TissuesIgA – MucosaIgE - Surfaces
• Master the concepts of Ig and Ab;
• Master the relationship between structure and functions of Ab;
• Master properties and biological activities of five classes of Igs.
Emphases
School of Medicine
Fudan University